<!DOCTYPE html>
<meta charset="utf-8">
<link rel="match" href="relative_position_vertical_percentage_ref.html">
<style>
body, html {
    margin: 0;
}
#a {
    height: 200px;
    width: 600px;
    background: gold;
}
#b {
    position: relative;
    top: 50%;
}
</style>
<div id=a><div id=b>X

